1. Technical Field
This invention relates to a flush toilet bowl and, more particularly, a flush toilet bowl of a type which discharges sewage by a syphoning action.
2. Background Art
In regard to such a type of flush toilet bowl, a wide variety of constructions have hitherto been known, a typical one being described in JP-U Sho-58-25381. The flush toilet bowl described in this publication is called the syphon jet type. The water discharge trap of the toilet bowl has a stepped part in a descending path and is transversely bent substantially at a right angle on the downstream side of the stepped part. Thereafter, a discharge opening opens vertically (hereinafter, such a discharge trap is referred to as a cross-laid type trap).
In this type of flush toilet bowl, the stepped part provided in the descending channel of the discharge trap causes a disturbance of water flow and forms the wall of water (seal), thereby producing a syphoning action. Hereupon, a principle of syphoning action will be explained. At the stage before flushing, the interior of the discharge trap is under an atmospheric pressure which is the same as that on the surface of the gathered water. The supplying of flushing water to this place causes the disturbance of water flow due to the stepped part, thereby forming a wall of water (seal) which closes one end of the trap.
When the supply of water continues in a condition of the seal being formed, air within the trap is discharged together with water and the pressure within the trap becomes negative with respect to the atmospheric pressure. This negative pressure causes a drawing force. As the discharge of air further proceeds, the trap is substantially filled with water and, at this time, the maximum drawing force occurs. Namely, a phenomenon of syphoning is produced by the initial seal, grows by the discharge of air and puts forth the maximum drawing force when the trap is filled with water. So, realizing the rapid production and growth of the syphoning action is important in order to save the amount of the flushing water.
Particularly, in the case where the position of the flush tank in the flush toilet bowl is attempted to be lowered for low-silhouetting the bowl, the potential energy of flushing water naturally becomes smaller, and so, in order to save an amount of flushing water, the realization of the above-described rapid production and growth of the syphon is all the more important. Moreover, ensuring a high capacity of water discharge is required.
Now, as a toilet bowl having a construction of air within the discharge trap being discharged early in order to ensure the early production of the syphon, there is one such type disclosed in U.S. Pat. No. 5,142,712.
This toilet bowl is provided with a cross-laid type discharge trap in a similar way to the toilet bowl disclosed in the above-described JP-U 58-25381. The cross-laid channel is bent upwardly before the discharge opening to provide a gathered water part before the discharge opening, in which a seal part is constituted. The air existing between the sealed water part and the above-described gathered water part is drawn under a negative pressure produced within the sealed tank by the discharge of the water within the sealed tank, so that the air within the trap is discharged, thereby ensuring the early production of the syphoning action. In this connection, the reason why a ventilation room is provided in the gathered water part in such a toilet bowl, is that there occurs the following disadvantage: If there is no ventilation room, because of the seal being always constituted at two points, a phenomenon of syphoning occurs in a considerably easy way. For example, in the case where a negative pressure occurs in the discharge pipe, such a negative pressure sucks and discharges not only the water in the gathered water part, but also the sealed water per se in the toilet bowl, so that odor from the discharge pipe reversely flows into the chamber by way of the bowl part of the toilet bowl.
However, the toilet bowl described in said U.S. Pat. No. 5,142,712 requires a sealed tank construction because of the utilization of the negative pressure within the tank. Further, connection of the downstream of the sealed water part to the interior of the tank produces the possibility of odor flowing into the tank, and so a separate construction for preventing such a possibility is required.
Accordingly, as to the construction of a toilet bowl, it is considered that the toilet bowl disclosed in U.S. Pat. No. 5,142,712 is conventionally used in combination with an ordinary tank which has no sealed construction and has only a function of gathering and discharging water; however, there occur problems as described below.
Since the sealed part is constituted only by the gathered water part, a large amount of water is required to close the above-described ventilation room, and it takes much time to produce a syphoning action; consequently, a large amount of flushing water is required. Making this ventilation room narrower is considered, however, there is a problem in that if it is made too narrow, the above-described disadvantages are apt to occur.
Further, an air pool is apt to occur in the inner portion of the descending channel of the trap and hinders the growth of a syphoning action, so, it is difficult to expect a sufficient effect in terms of the early production of a syphoning action in spite of the adoption of the sealed construction due to the gathered water part.
Moreover, since the weir between the rising channel of the discharge trap and the descending channel of the discharge trap is bent substantially at a right angle, the water which has passed through the weir comes off the weir and collides with the side wall at the back of the descending channel of the trap before it reaches the gathered water part, thereby forming water turbulence which swallows up the air within the trap. Further, it takes much time to discharge the air within the trap.
In addition, there was a problem in that in the cross-laid type of trap, water stream changes from the transverse direction to the vertical direction before the discharge opening in view of its construction; however, a change of direction of the water stream at this portion is not smoothly performed and a force of water discharge from the discharge opening is reduced.
Further, it is empirically known that the thinner the diameter of the discharge trap is, the earlier the production of the syphoning action is, however, if the diameter of the trap is made too thin, clogging of sewage is apt to occur and the primary function of the toilet bowl is adversely affected. Moreover, a large change in the diameter of the discharge trap causes a large loss of energy. Therefore, when the syphoning action is produced, a force of suction due to the syphoning action does not become great, and an increase in the flushing capacity cannot be expected.
In regard to another type of flush toilet bowl, a low-silhouette type of flush toilet bowl having a flush tank, in which flushing water is stored, disposed in a position lower than the toilet bowl body, is generally regarded as a high grade flush toilet bowl. Such a type of flush toilet bowl in the past includes the one which is described in JP-A Sho-64-75740. The toilet bowl described in this publication is a toilet bowl of a so-called syphon vortex type in which a syphoning action and a vortical action are used in combination. A decrease in the force of water supplied to the tank due to the fact that the position of the top of the flush tank B is lowered, as shown in FIG. 27, to suppress the water level of the flushing water from a rim surface 3a of the toilet bowl body A in a lower level, is supplemented in such a way that the flush tank B is positioned lower than the rim surface 3a to thereby increase the capacity of the tank to make an amount of water used at the time of flushing larger, thereby ensuring a total amount of discharge of 16 liters or so (total amount discharged from the toilet bowl to the discharge pipe in a single usage).
In the meantime, the requirement of water saving for the flush toilet bowl has gradually come to be a strict one in recent years, particularly, in the U.S.A. it has become strict to such a degree that a regulation limits the total amount of discharge to 1.6 gallons (6 liters). Therefore, it is difficult to save water while ensuring the flushing capacity using the syphon-type toilet bowl having a conventional construction, and it is particularly difficult to cope with such a requirement with the low-silhouette type toilet bowl.
The present invention has been made taking the above-described problems in the prior arts into consideration, and aims at providing a flush toilet bowl which can sufficiently cope with the strict requirements of water saving in recent years and allows a sufficient flushing capacity to be displayed.